As you can see there's 3 types of files on a DVD: .VOB, .IFO and .BUP:

VOBs - Video OBjects

A VOB contains several streams multiplexed together: Video, Audio and Subtitles.
Video is MPEG-2, audio can be AC-3, Linear PCM, Mpeg 2 multichannel or MPEG1
layer2 2 channel audio. AC3 is pretty much the standard and MPEG-2 multichannel
can only be found on very few discs (one example is "In the line of fire,
PAL edition") as this format was initially considered to be the standard
format in Region2 (Europe and Japan) but was later dropped. PCM is mostly found
on music DVDs and MP2 on cheaper productions. PCM is high quality uncompressed
audio which takes a lot of space, hence it's not an ideal choice for full length
movies with extras and possibly multiple languages. AC3 streams have a bitrate
between 192 and 448kbit/s. 192kbit/s is used for 2 channel sound, and 384-448kbit/s
for 5.1channel surround.

A VOB can contain one main video stream and several multiangle streams, allowing
you to switch (as an example) the perspective during the movie. This feature
is mostly used to display storyboards or other extra features during playback.
The maximum bitrate of the video stream is 9.8mbit/s. Together, video and audio
stream must be below 10mbit/s at any given moment. It's possible to have up
to 9 different audio streams and you can usually switch the audio stream during
playback (this feature can be disabled during the authoring phase of a DVD).
It's also possible to have up to 32 different subtitle streams. Subtitles are
4 color bitmaps which are overlayed over the video stream, they're usually not
encoded into the video stream.

As said before there's usually just one video stream and it always has ID 0xE0.
PTS is the Program Time Stamp and states when a certain stream starts with respect
to the beginning of the VOB. As you can see the resolution is 720x480 so it's
an NTSC DVD. The frame-rate of 29.97 basically states the same fact. The DAR
of the stream is 16:9. Then there's 4 audio streams: 0x80 - 0x83. Note that
these are AC3 streams. All AC3 streams are in stream 0xBD, substreams 0x8x.
When there's a DTS stream it usually has stream id 0xBD 0x88 or 0xBD 0x89. PCM
streams are also located in stream 0xBD, they have stream IDs 0xAx, from 0xA0
up to 0xA9. MP2 audio finally is located in the stream 0xCx. Here's an example
from a PCM and MP2 stream:

There are also 2 substreams, 0x20 and 0x21. All subtitle streams are located
in the 0xBD stream as well.

Furthermore there are usually padding streams (0xBE) but they don't concern
us.

You might also have noticed the VOB and Cell IDs. A Cell is the smallest unit
on a DVD. On a simple DVD this usually represents a chapter but it gets more
complicated in many discs. If you're interested about Cells on a DVD I suggest
you start learning how to use Scenarist, because only then will you truly understand
how these works. When it comes to VOB IDs I still haven't found how they are
created exactly and to what kind of structure they correspond. Usually each
unit on its own has its own VOB ID, for instance the main movie and the trailer.
In multiangle and seamless branching titles each angle has its own VOB ID.

IFOs - InFOrmation

IFO Files give the player important navigational information, like where a
chapter starts, where a certain audio or subtitle stream is located, etc. This
is the reason why it's only possible to rip certain parts of a movie (like a
chapter) with a ripper which can read this files.

Or old friend vStrip can and let's have a glimpse at the output we get when
using ifo parsing (sample command line: vStrip f:\video_ts\vts_02_1.vob -if:\video_ts\vts_02_0.ifo)

As you can see there's 2 PGCs or ProGram Chains in this movie. PGC 0 represents
the main movie whereas PGC 1 the studio logo at the beginning. This structure
might be a lot more complicated but usually it's as easy as shown above. Multiangle
movies will give you several PGCs having the same length, and seamless branching
movies several PGC with different length. By selecting the right PGC you can
get the right version of the movie. Also.. the PGC corresponds to the Title
number being displayed in your player. Here's just an example (Matrix - follow
the white rabbit feature = Title 6 or in other words PGC 5 since the PC starts
counting at 0 internally).

Last but not least IFO files are not encrypted.

BUPs - BackUP

BUP files are just backup files off the IFOs. As their counterparts they are
not encrypted.

Look closer

Now that we know what each filetype is for let's look at the actual example
again:

The VIDEO_TS.* files represent the first play item. This is an item being set
during authoring and is the first thing being played when the disc is inserted
in the player. Usually this is just a copyright notice, but it could also be
a menu where to select the language of the menu, some trailers, etc. The video_ts.vob
contains the video and audio data, the video_ts.ifo the navigational data and
video_ts.bup is the backup for video_ts.ifo.

There's 2 more ifo files: vts_01_0.ifo and vts_02_0.ifo. The first 2 numbers
in the name tell the title number. vts_01_* is title 1, vts_02_* title 2, etc.
Obviously there can be 99 titles at the maximum (vts_00_* does not exist). Each
title can have 10 VOB files, whereas the first VOB (vts_XX_0.vob) always contains
the menu for that title. Each title has at least 2 VOBs (one for the menu and
one for the main feature) and exactly one ifo and bup file.

In our case title 1 contains the behind the scenes featurette and has its own
menu. Title 2 contains the main movie, also with its own menu.

As you can see the maximum size of a VOB file is 1GB. In fact the files must
be smaller than or exactly one GB (1024x1024x1024Bytes), but there are certain
which aren't and these can't be played on a PC.

Now the last question: how to locate the main movie on a disc? The largest
.ifo file will give you the title number and then you need all the VOB files
except for the menu VOB (unless you want the menu as well, of course). Most
Rippers (if they don't do ifo parsing) proceed according to this rule to select
the main movie and the ifo to be copied.

Inside a VOB

DVD video content is broken into titles (movies or albums) and parts of titles
(chapters or songs). Titles are made up of cells linked together by one or more
Program Chains (PGCs). A cell is the smallest video unit on a DVD. Often a cell
is equal to a chapter but not always. Cells are sometimes grouped together using
VOB IDs. Examples are Warner Brothers movies where the main movie has one VOB
ID on one layer and another one on another layer, multiangle movies (at the
branching points each angle gets its own VOB ID, and then when they get back
together we have the next VOB ID, etc., and seamless branching movies - where
we have different VOB IDs for the different parts of movies that are selected
to play when selecting a certain playback option).